Most traditional radio architectures operate on a single band or range of frequencies. There are many applications, however, where multiple bands need to be monitored. For example, in radio surveillance the entire spectrum may need to be monitored because content is spread throughout the spectrum on individual frequency bands. Where such wideband monitoring is required, the norm is to utilize multiple radios, each designed to operate in one specified band, or use a wideband digitizer with an analog to digital converter (ADC) sufficient to the task. When attempting to operate a wideband digitizer in a dense signal environment, however, the ADC can very easily be driven past its dynamic range by a momentary power spike in any one of the signals. When this happens all the signal content is lost until the ADC and subsequent digital signal processing (DSP) recovers from the ADC overload. Alternatively, a momentary power spike in any one of the stronger signals could overpower and drown out a weaker signal, which may contain important content.
The resolution of the ADC determines the dynamic range of the radio receiver, and the current state of the art for ADCs is simply insufficient to digitize, for example, a 0-3 GHz spectrum, the bandwidth on which all the relevant cellular communication resides, because sampling the spectrum would require a 6 GHz sampling frequency, well beyond the current state of the art.
The current state-of-the-art performance of an ADC has a 12 to 16 bit resolution at 3 GHz to 500 MHz clock rates, respectively, corresponding to a dynamic range of approximately 74 db to 98 db, respectively. This, however, is merely the theoretical dynamic range; in reality it is 6 db or less due to implementation inefficiencies. Radios typically require a dynamic range of 100 to 150 db, corresponding to a lower limit of approximately 17 bits and an upper limit of 25 bits, with the nominal required performance somewhere in the middle at 21-22 bits resolution. Such ADCs do not exist today.
Therefore, a solution is needed to reduce the size and the number of ADCs necessary for wideband digitization.